Catálogo de publicaciones - libros

In this paper we introduce a new tool that hides whether or not an “encryption” algorithm actually performs encryption or not. We call this a computational questionable encryption scheme and show how it can be used to devise mobile agents that conceal whether they encrypt or delete data prior to data transmission. Such agents may be useful in the honest-but-curious setting in which the author of the agent wishes to keep confidential whether or not the agent collects and transmits data while in transit. Informally, a questionable encryption scheme adds a “fake” key generation algorithm to a PKCS. The key generation algorithms of a computational questionable encryption scheme produce a “public key” and a poly-sized witness . Depending on which of the two key generation algorithms the user decides to use, is real or fake. When the cipher is supplied with a real then it produces decipherable ciphertexts and proves this. When the cipher is supplied with a fake then it produces indecipherable ciphertexts (with respect to ) and proves this. We call the former a witness of encryption and the latter a witness of non-encryption. We formally define the notion of a computational questionable encryption scheme and present a construction for it based on the ElGamal cryptosystem. We prove the security based on the Decision Diffie-Hellman problem and a reasonable new intractability assumption in the random oracle model. Finally, we show how a computational questionable encryption scheme is related yet different from all-or-nothing disclosure of secrets and related notions.

We present an algorithm for embedding robust reversible watermarks into CAD models that are represented by a collection of NURBS (Non Uniform Rational B-Spline) surface patches.

Changes to the geometry of the surface representation are introduced by moving one control point per surface patch. This approach provides robustness against converting the model into the mesh representation. The information needed to restore the original control point location is added to the knot vectors of the patch, thus enabling recovery of the original model from the watermarked NURBS representation.

We exploit the properties of the NURBS representation for preserving the continuity between adjacent patches. Continuity is the major criterion of designers for assessing the quality of surface models.

This paper presents a high-capacity data hiding method for 3D polygonal meshes. By slightly modifying the distance from a vertex to its traversed neighbors based on quantization, a watermark (i.e., a string of binary numbers) can be embedded into a polygonal mesh during a mesh traversal process. The impact of embedding can be tuned by appropriately choosing the quantization step. The embedded data is robust against those content-preserving manipulations, such as rotation, uniformly scaling and translation, as well as mantissa truncation of vertex coordinate to a certain degree, but sensitive to malicious manipulations. Therefore, it can be used for authentication and content annotation of polygonal meshes. Compared with the previous work, the capacity of the proposed method is relatively high, tending to 1 bit/vertex. Besides to define the embedding primitive over a neighborhood so as to achieve resistance to substitution attacks, the security is also improved by making it hard to estimate the quantization step from the modified distances. A secret key is used to order the process of mesh traversal so that it is even harder to construct a counterfeit mesh with the same watermark. The numerical results show the efficacy of the proposed method.

In 2005, Germany introduced a new Amateur Radio Ordinance prohibiting encrypted radio traffic at home. Crypto-bans can be circumvented using steganography. However, present steganographic methods are not eligible because the embedded message will not survive the usual distortions in a radio transmission. Robust as current watermarking methods are, they leave clearly detectable traces and have a smaller capacity.

This paper presents measures that improve the robustness of steganographic communication with respect to non-intentional, random channel errors and validates their effectiveness by simulation. For the scenario of a radio communication, we determine practicable parameters for least detectability under six different short wave conditions. The resulting method embeds messages with a length of up to 118 bytes in a narrow-band Slow Scan Television connection in Martin-M1 mode.

Tamper-resistant software (TRS) consists of two functional components: tamper detection and tamper response. Although both are equally critical to the effectiveness of a TRS system, past research has focused primarily on the former, while giving little thought to the latter. Not surprisingly, many successful breaks of commercial TRS systems found their first breaches at the relatively naïve tamper-response modules. In this paper, we describe a novel tamper-response system that evades hacker detection by introducing delayed, probabilistic failures in a program. This is accomplished by corrupting the program’s internal state at well-chosen locations. Our tamper-response system smoothly blends in with the program and leaves no noticeable traces behind, making it very difficult for a hacker to detect its existence. The paper also presents empirical results to demonstrate the efficacy of our system.

Self-modifying code is notoriously hard to understand and therefore very well suited to hide program internals. In this paper we introduce a program representation for this type of code: the state-enhanced control flow graph. It is shown how this program representation can be constructed, how it can be linearized into a binary program, and how it can be used to generate, analyze and transform self-modifying code.

In this paper, a novel steganalysis scheme is presented to effectively detect the advanced JPEG steganography. For this purpose, we first choose to work on JPEG 2-D arrays formed from the magnitudes of quantized block DCT coefficients. Difference JPEG 2-D arrays along horizontal, vertical, and diagonal directions are then used to enhance changes caused by JPEG steganography. Markov process is applied to modeling these difference JPEG 2-D arrays so as to utilize the second order statistics for steganalysis. In addition to the utilization of difference JPEG 2-D arrays, a thresholding technique is developed to greatly reduce the dimensionality of transition probability matrices, i.e., the dimensionality of feature vectors, thus making the computational complexity of the proposed scheme manageable. The experimental works are presented to demonstrate that the proposed scheme has outperformed the existing steganalyzers in attacking OutGuess, F5, and MB1.

Conventional steganalysis aims to separate cover objects from stego objects, working on each object individually. In this paper we investigate some methods for pooling steganalysis evidence, so as to obtain more reliable detection of steganography in large sets of objects, and the dual problem of hiding information securely when spreading across a batch of covers. The results are rather surprising: in many situations, a steganographer should spread the embedding across all covers, and the secure capacity increases only as the square root of the number of objects. We validate the theoretical results, which are rather general, by testing a particular type of image steganography. The experiments involve tens of millions of repeated steganalytic attacks and show that pooled steganalysis can give very reliable detection of even tiny proportionate payloads.

In this paper, we study embedding efficiency, which is an important attribute of steganographic schemes directly influencing their security. It is defined as the expected number of embedded random message bits per one embedding change. Constraining ourselves to embedding realized using linear covering codes (so called matrix embedding), we show that the quantity that determines embedding efficiency is not the covering radius but the average distance to code. We demonstrate that for linear codes of fixed block length and dimension, the highest embedding efficiency (the smallest average distance to code) is not necessarily achieved using codes with the smallest covering radius. Nevertheless, we prove that with increasing code length and fixed rate (i.e., fixed relative message length), the relative average distance to code and the relative covering radius coincide. Finally, we describe several specific examples of -ary linear codes with matched to the embedding operation and experimentally demonstrate the improvement in steganographic security when incorporating the coding methods to digital image steganography.

We provide construction of steganographic schemes secure against adaptive chosen stegotext attacks. Our constructions achieve embedding rate equals to the Shannon entropy bound on steganographic channel capacity. Further the covertext distribution can be given as either an integrable probability function or as a random covertext sampler. We also introduce steganographic codes that are of interests in constructing other steganographic protocols such as steganographic secret sharing or steganographic distributed computations.